1. Field of the Invenion
The invention relates to the field of non-aqueous electrochemical cells and, more particularly, to solid halogenated organic depolarizers for a high-rate non-aqueous electrochemical cell.
2. Description of the Prior Art
Much work has been done in the field of high energy battery systems utilizing highly reactive anode materials such as alkali metals in combination with non-aqueous electrolytes. The electrolyte is normally composed of a solute which is commonly a metal salt or a complex metal salt of group I-A, II-A or III-A elements of the Periodic Table dissolved in a compatible non- aqueous solvent. The batteries often are used in applications which require them to be operable over a wide temperature range with a high output over that wide temperature range. For this reason, much research has been conducted concerning the development of solvent- solute pairs which are stable and have a high ionic conductivity over a wide temperature range. In addition, it is desirable that the chemical system of the electro- chemical cell have a long, stable shelf life when used in a primary or secondary battery system. The prior art is replete with many examples of such high capacity or high rate cells which utilize solvents containing sulfur dioxide (SO.sub.2), thionyl chloride (SOCl.sub.2) and sulfuryl chloride (SO.sub.2 Cl.sub.2). These compounds, along with certain other oxyhalides, are normally used in combination with an alkali metal anode or alkaline earth metal anode and an electrolyte consisting of a salt of a cation of the metal of the anode together with the solvent materials.
The basic problem with the electrochemical cells of the prior art utilizing sulfur dioxide, thionyl chloride or sulfuryl chloride has been the problem with safe storage and operation of the batteries. Under certain circumstances, the batteries tend to experience thermal runaway in which reactions and pressure buildup within the cell may actually cause a very violent explosion. One reason for this occurrence has been traced to reactions which occur between the metal anode and the sulfur of the solvent material. In addition, because sulfur dioxide is a gas at ordinary temperatures, overheating or the use of such batteries at higher temperatures may lead to the buildup of excessive pressure within the cell.
One prior art solution to this problem has been the provision of a liquid organic solvent depolarizer system which eliminates the need for any sulfur- containing compounds in the system. A example of this is formed in U.S. Pat. No. 4,439,503. Another U.S. Pat. No. 4,132,837 discloses the use of macroheterocyclic organic compounds to stabilize organic polar aprotic solvents in such a system.
Another approach has been to use solid cathode depolarizers. In the prior art several inorganic solid cathode depolarizers such as MnO.sub.2, FeS.sub.2, CuS and Ag.sub.2 CrO.sub.4 have been used successfully in active metal, non-aqueous cells. But cells using lithium anodes and CuS or FeS.sub.2 have generally low operating voltages, i.e., less than 1.6 volts and 2.0 volts, respectively, even at very low discharge rates. Cells, employing MnO.sub.2 or Ag.sub.2 CrO.sub.4 in combination with lithium anodes have a higher operating voltage of about 2.8 volts. It has been found, however, that the Li/MnO.sub.2 cell voltage drops during discharge and the Li/Ag.sub.2 CrO.sub.4 cells are very expensive in comparison.